1. Field of the Invention
The present invention relates generally to the calibration of fluid meters and, more particularly, to a system to permit in situ calibration of small gas meters such as residential gas meters.
2. Description of the Prior Art
In the prior art, large commercial or industrial gas meters have conventionally been provided with test ports in the meter which are accessible for calibration and verification of the meter while the meter is still in service. However, small capacity meters such as those associated with residential installations have not been provided with any means of calibrating the meters while in use. In order to calibrate the conventional residential or other small gas meter, it has heretofore been necessary to remove the meter from the line, replace it with a previously calibrated meter, and to conduct the meter testing at a remote location. This has been done on a regularly scheduled basis, for example, every five years, by most gas utility companies at great expense. Many of these meters have needed only a simple verification or minor adjustment which could easily have been accomplished if the meter could have been checked in situ without interruption of the gas supply to the customer.
Ultrasonic flow measurement is one approach that has been tried successfully for the measure of liquid flow in regard to verifying or calibrating liquid meters. However, because of power transmission losses at the boundary layer in gaseous flow, the technique of attaching ultrasonic probes to the gas pipes introduces errors which have not allowed this technique to be used successfully in that regard. Thus, there exists a definite need for the ability to verify and calibrate a relatively small gas meter such as a residential gas meter in situ without interruption of the gas flow to the consumer.